There are also good reads on the thread Short book / advanced middle school level.

And on this recent blog post from Gifted Parenting Support:
Finding Age Appropriate Books for Gifted Readers
by L J Conrad
July 6, 2015

Adding a link to the thread Graphic novel recommendations? which mentions a 9-year-old.

Adding a link to the thread Books like Horrible Histories for older kids.

Adding a link to the thread Book Recommendations For All Ages, which mentions a book for
"advanced fourth graders and up."

Adding a link to the the thread Non-fiction audio book recommendations, for a 10-year-old child.